In an announcement Wednesday, his office said the 74-year-old is being treated for "localized prostate cancer.''

University of California San Francisco oncologist Eric Small said in a statement released by the governor's office that the cancer was in its early stages.

He said it is being treated with a short course of conventional radiotherapy. He called the governor's prognosis excellent.

The National Cancer Institute estimated there were 241,740 new cases of prostrate cancer in the United States so far in 2012 resulting in 28,170 deaths.

Prostate cancer is the most common cancer in men. More than 90 percent of the cases are caught in the early stage, and nearly all men with such diagnoses survive at least five years.

This is Brown's second bout with cancer. He underwent minor surgery in spring 2011 to remove a cancerous growth on his nose.

Here's the complete statement from the governor's office:

The Governor’s Office today announced that Governor Brown is undergoing treatment for localized prostate cancer.

Dr. Eric Small, Brown’s oncologist at UCSF, issued the following statement: “Fortunately, this is early stage localized prostate cancer, which is being treated with a short course of conventional radiotherapy. The prognosis is excellent, and there are not expected to be any significant side effects.”

Governor Brown is continuing a full work schedule during the treatment, which is expected to be completed the week of January 7, 2013.

Typical radiation treatment for an early stage prostate cancer is five days a week for four to five weeks, said Dr. Ralph de Vere White, urological oncologist and director of the UC Davis comprehensive cancer center in Sacramento.

Not all men who are diagnosed with the disease choose to undergo treatment, and doctors advise patients to consider the risks.

De Vere White, who is not involved in Brown's case, said given the governor's otherwise excellent health, it's an easy decision to do the radiation treatment.

"When you're as healthy as the governor is, and you are looking out at 10 years, then you go for a treatment that is going to have in excess of a 97 percent cure rate,'' he said. "It really should have very minimal side effects, should have minimal to no interference with his life, and kind of represents the reason why people advocate for finding this disease early.''

Brown previously served as California governor from 1975 to 1983. He was mayor of Oakland from 1999 to 2007 and served as California attorney general before being elected governor again in November 2010.